Problem Solving. Software Engineering. Behavior. OCD in a Nutshell. Behavior. Objects Operations Algorithm. Object-Centered Design

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Software Engineering

(Chap. 1)

Object-Centered Design

When we prepare a program, the experience can be just

like composing poetry or music … My claim is that it is

possible to write grand programs, noble programs, truly

magnificent ones! ... Computer programming is an art.

-

Donald Knuth, “Programming as an Art”, 1974

Problem Solving

Let’s solve this

temperature-conversion problem

:

Write a program that, given a temperature in

Celsius, displays that temperature in Fahrenheit.

5 Phases of Software Life Cycle:

•Problem Analysis and Specification

•Design

•Implementation (Coding)

•Testing, Execution and Debugging

•Maintenance

OCD (Object-Centered Design)

2

OCD in a Nutshell

• Behavior

• Objects

• Operations

• Algorithm

Behavior

A. Describe the desired behavior of the program:

Our program should display a prompt for the

Celsius temperature on the screen, read that

temperature from the keyboard, compute the

corresponding Fahrenheit temperature, and

display that temperature along with a descriptive

label on the screen.

4

Using

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Objects

B. Identify the

nouns

in the behavioral description:

Our program should display a prompt for the

Celsius temperature on the screen, read that

temperature from the keyboard, compute the

corresponding Fahrenheit temperature, and

display that temperature along with a descriptive

label on the screen.

These make up the

objects

in our program.

5

Using

OCD

Operations

These make up the

operations

in our program.

C. Identify the

verbs

in the behavioral description:

Our program should display a prompt for the

Celsius temperature on the screen, read that

temperature from the keyboard, compute the

corresponding Fahrenheit temperature, and

display that temperature along with a descriptive

label on the screen.

6

Using

OCD

Algorithm

D. Organize the objects and operations into a sequence

of steps that solves the problem, called an

algorithm

.

1 . Ask

the screen

to display

a prompt

for

the Celsius

temperature

on

the screen

.

2 . Ask

the keyboard

to read

the temperature

.

3 . Compute

the Fahrenheit temperature

from

the Celsius

temperature

.

4 . Ask

the screen

to display

the Fahrenheit temperature

,

plus an

informative label

on

the

screen

.

7

Using

OCD

Don’t even think about coding until

you’re sure of your algorithm.

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Coding

• We now translate the algorithm into an HLL.

• Use the features of the Java language to:

–

represent our objects

–

perform our operations

• Java provides two implementation methods:

–

Java

applications

–

Java

applets

(Sec. 1.3)

Java Applications

• Programming languages traditionally allow

programmers to write stand-alone

applications.

• In Java, these are called

applications

.

Compiler

A Java Application

Program The byte-code for_{the application}

Interpreter

javac

java

Abc.java

_Abc.class

Representing Objects

Determine a

type and name for each object

:

ObjectJava TypeNamethe programa promptthe Celsius temp.the screenthe keyboardthe Fahrenheit temp.a label

ObjectStringdoubleScreenKeyboarddoubleString

Temperature--celsiustheScreentheKeyboardfahrenheit

--Performing Operations

Identify the Java operator to perform a given

operation, if there is one…

OperationLibrary?Name

Display a stringRead a doubleCompute fahrenheitDisplay a double

ann.easyioann.easyio--ann.easyioprint()readDouble()--print()

To compute the Fahrenheit temperature, we need to find the

Celsius to Fahrenheit formula in a reference book...

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Operations (Revised)

Operation

Library?

Name

Display a string

Read a double

Compute fahrenheit

Divide two ints

Multiply two doubles

Add two doubles

Display a double

ann.easyio

--

built-in

ann.easyio

print()

readDouble()

--

/

*

+

print()

We can now add more detail to the

computation:

doubles

/* Temperature.java converts Celsius * temperatures to Fahrenheit. * Author: Keith Vander Linden * Date: 2 June 2001

* Modified: L. Nyhoff, Sept. 2002 */

import ann.easyio.*; // Screen & Keyboard classes class Temperature extends Object

{

public static void main(String [] args) {

Screen theScreen = new Screen();

theScreen.print("Welcome to the temperature converter!\n" + "Please enter the temperature in Celsius: "); Keyboard theKeyboard = new Keyboard();

double celsius = theKeyboard.readDouble(); double fahrenheit = ((9.0/5.0)*celsius) + 32; theScreen.print(celsius + " degrees Celsius is " +

fahrenheit + " degrees Fahrenheit.\n" + "It's been a pleasure!\n");

} }

The Code

Objects? Operations?

COMPILATION HINT

• Use the tools available to you.

• Specifically, use

M-x compile

in xemacs.

–

Use

C-x `

to run through the error messages.

ß

Xemacs will automatically go to the next message.

ß

It will even load in the proper file and go to the

offending line.

ß

Why do you want to do this work?

–

Run only one session of xemacs; open multiple

files into the same session.

–

If you aren't comfortable or used to it, practice.

(or middle mouse button)

import ann.easyio.*; // Screen & Keyboard classes

class Temperature extends Object {

} }

Documentation

Always begin a file

with an

opening

comment

similar to this.

.

3 Kinds of Comments:

/*...*/ multi-line comment // single-line comment

-- indicate what classes of a package are used. -- explain obscure code

/**...*/ Javadoc multi-line comment javadoc program extracts these into special documentation.format

-- see Java'sAPI (Section 2.4)

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} }

Import Section

This loads the Java

packages that we need.

Packages:

-- Groups of related classes e.g., easyio

-- Often grouped into libraries

e.g., ann

-- Java has > 1600 classes grouped into several packages -- see its API

Use

import package_name.*;

to make classes in a package easily accessible

}

The Class Definition

Java programs are classes

built upon existing classes

Form:

class Class_name extends Object {

public static void main(String[] args) {

statements

} }

-- Use meaningful class name -- Capitalize it

-- Save program as Class_name.java

{

}

The Main Method

Java applications begin

execution by running

main()

{

theScreen.print("Welcome to the temperature converter!\n" + "Please enter the temperature in delsius: ");

Keyboard theKeyboard = new Keyboard(); double celsius = theKeyboard.readDouble(); double fahrenheit = ((9.0/5.0)*celsius) + 32; theScreen.print(celsius + " degrees Celsius is " +

} }

Step 1

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{

theScreen.print("Welcome to the temperature converter!\n" + "Please enter the temperature in Celsius: ");

Keyboard theKeyboard = new Keyboard(); double celsius = theKeyboard.readDouble();

double fahrenheit = ((9.0/5.0)*celsius) + 32; theScreen.print(celsius + " degrees Celsius is " +

} }

Step 2

Read the Celsius temperature.

{

double celsius = theKeyboard.readDouble();

double fahrenheit = ((9.0/5.0)*celsius) + 32;

theScreen.print(celsius + " degrees Celsius is " + fahrenheit + " degrees Fahrenheit.\n" + "It's been a pleasure!\n");

} }

Step 3

Calculate the

Fahrenheit temperature.

{

double celsius = theKeyboard.readDouble(); double fahrenheit = ((9.0/5.0)*celsius) + 32;

theScreen.print(celsius + " degrees Celsius is " + fahrenheit + " degrees Fahrenheit.\n" + "It's been a pleasure!\n");

} }

Step 4

Display the results.

Running the Program

You can now run your application:

Welcome to the temperature converter!

Please enter the temperature in Celsius: 20

20.0 degrees Celsius is 68.0 degrees Fahrenheit.

It's been a pleasure!

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